Method of making paper stiffened with waste pulp liquor solids



United States Patent 3,305,435 METHOD OF M AlKlNG PAPER STIFFENED WITH WASTE PULP LIQUOR SOLIDS Edward M. Williston, Longview, and Arthur S. Gregory and Clark C. Heritage, Tacoma, Wash., assignors to Weyerhaeuser Company, Tacoma, Wash, a corporation of Washington No Drawing. Continuation of abandoned application Ser. No. 236,143, Nov. 7, 1962. This application July 7, 1966, Ser. No. 563,619

6 Claims. (Cl. 162117) This application is a continuation of Serial No. 236,143 filed November 7, 1962, and now abandoned.

This invention relates to the paper making art, and more particularly to a paper made from the common species of cellulosic materials and characterized by a high degree of stiffness and structural strength, and to the method of its manufacture.

Conventional methods of providing stiffened papers heretofore have involved the use of special cellulosic pulps which impart inherent stiffness to the paper, or the coating or impregnation of conventional paper stocks with special stiffening agents. However, these methods are economically disadvantageous in the following respects: The special cellusosic pulps are too costly for the limited degree of improvement which they impart to the paper. The special stiffening agents either are too costly or they present such problems as hazardous and difficult application, unfeasible waste recovery, poor glueability, and fragility of a treated paper.

For example, sodium silicate has been employed as a low cost stiffening agent, but the treated paper is too brittle for such uses as corrugated medium. Additionally, the treated paper exhibits poor glueability, and hence is not practical for such uses as liner for corrugated box material. Sulphur has been used as a stiffening agent, and although its unit cost is reasonably low, the large amount required to be added to paper to achieve a reasonable degree of stiffness reflects an excessive cost to the finished product. Moreover, it is extremely hazardous and difiicult to apply, its waste recovered is not economically feasible, and the treated paper exhibits poorer glueability.

Synthetic resins of various types also have been employed as special stiffening agents, and while they impart to the paper all of the physical characteristics desired, their high cost renders the product economically undesirable.

Accordingly, it is the principal object of the present invention to provide a stiffened paper from common species of cellulosic fibrous sources by a method which utilizes low cost raw materials, which may be performed in conjunction with conventional types of paper making machinery at conventional production speeds, and which is capable of increasing the stiffness of the paper without adversely affecting its strength or other desirable properties.

The foregoing and other objects and advantages of this invention will appear from the following detailed description.

In its broad concept, the present invention involves the impregnation of the cellulosic fiber of paper after formation of the sheet, with a treating solution consisting essentially of aqueous waste pulp liquors. Preferably, the

solution is applied to one or both sides of a preformed sheet of paper stock, after the latter has been drained or dried, and the application is made in such manner as to effect pickup of from 0.5 to 15% or more liquor solids by weight, dry sheet basis.

The method of this invention is applicable to any of the conventional paper making pulps derived from wood, straw, bagasse, cane and like lignocellulose materials.

Further, it is applicable to pulps made by chemical, semichemical or mechanical methods.

The waste pulp liquor may be obtained from various conventional pulping processes. Thus, for example, there may be used the sulfite liquors of ammonia, calcium, magnesium and the alkali metals. Also usable are the alkali liquors of the kraft and other processes. The liquors may be used as such or may be dried and the dried solids redispersed in water. Also, desugared lignin or other lignin fractions produced from waste liquors may be used.

The liquors may be treated for reduction of their content of reducing sugars to not more than 1%. Although the presence of such sugars does not appear to affect adversely the concora improvement of the paper, it does appear that the presence of sugars decreases to a small degree the glueability of the treated paper.

The solids content of the liquor may range from 5 to 25%, preferably about 15%, the upper limit being determined primarily by the viscosity of the solution at its application temperature. In general, the application temperature may vary between ambient temperature and the boiling point of the solution, preferably between 70 and C. It is desirable that the solids content and temperature of the solution be as high as practicable, While providing a viscosity sufficiently low for effective application.

It is also desirable that the paper sheet be formed from an aqueous slurry of fibers in such manner as to provide the characteristics of freeness, Cobb and porosity, consistent with its ultimate strength requirements, that give to the paper a high ability to pick up the aqueous liquor solution. In this latter regard, liquor solids pickup into the paper may range from 0.5 to more than 15% dry fiber basis.

It has been found effective to add the liquor in the vicinity of the size press. Application of the liquor may be effected by dipping the paper in the solution, or by depositing the solution upon one or both surfaces of the paper by means of spray nozzles or rolls.

Conveniently, the solution is applied intermediate the ends of the drier roll assembly, at a point where a sufficient number of drying rolls still remain to achieve proper reduction in moisture content of the paper. Thus, for example, in a conventional drying assembly of about 50 rolls, the solution may be applied in the vicinity of the 40th roll.

It will be understood that the feed rate of solution to the paper, to achieve a desired degree of pickup, varies with the web speed, characteristics of the paper sheet being formed, solids content of the solution, and other factors.

The treated paper may be employed per se for various commercial applications, such as liner for the production of corrugated box board. It may also be used as the corrugated medium, in which case the treated paper is passed through conventional corrugating apparatus. In this latter regard it has been found helpful to precondition the sheet with a greater amount of steam than ordinarily employed, to assure uniformity of moisture content throughout the sheet and to provide a slightly higher temperature in the sheet for most effective results at the fluting rolls.

The corrugated paper then is passed through conventional glue applying apparatus where glue is applied to the crests only of the corrugated medium. Face sheets then are applied to the opposite sides of the corrugated medium and the assembly pressed and cut to appropriate lengths.

Illustrative examples of the present invention are contained in Table I. The various treating solutions were applied at a temperature of about F. at the size press to one side of 26 pound neutral sulfite semi-chemi- J cal corrugating medium, and at a web speed of about 200 feet per minute. The treated sheets were dried and preconditioned, along with untreated control sheets, at 50% relative humidity and 70 F. for approximately 24 hours, before testing for concora. The control sheets had a concora of 66.3 points.

TABLE 1 Solution Solids Aqueous Solution Solids, Pickup. Coneora Percent by Percent by Weight Weight Calcium Lignosullonate (not desugarizcd) (1) 15 .4 80.8 (2) 15 3.6 87.9 Calcium Lignosull'onate (desu garized) l5 3. 4 87. 8 Sodium Lignosullonate (not desugarized) 15 2. 7 89. 6 Sodium Lignosull'ouate (desugarizcd) a. (1) 15 1.0 83.4 (2) 15 3.3 87.9 Ammonium Lignosullonate (not desugarizcd) 15 1. 2 85. 5 Sulfito Red Liquor-Mg. base (not (lesugnrized) 11 5. 4 87.7 Kraft Black Liquor (not desugarized) 11 2. 9 87. 6 Sodium salt or Alkali Ligniu (dcsugarized) 15 2. 6 86. 1

As other examples, 28 pounds kraft pulp was made into a sheet on a conventional paper machine and, after draining and drying was treated with waste calcium sulfite liquor and with magnesium liquor by spraying onto the surface of the sheet. The solids content of the liquors was 13.0% and 14.5% respectively and the solids pickup in the paper was about 14% in each instance. The resulting concoras were 102 and 99 points respectively compared with the control sheet concora of 60 points.

From the foregoing it will be apparent that by the present invention papers produced from the common species of cellulose fiber material may be stilfening to a substantial degree at minimum cost, rendering the treated paper suitable for many commercial uses including the production of corrugated medium and liners. Production costs are further minimized by enabling the process to be integrated into conventional paper making processes with minimum additional equipment.

It will be apparent to those skilled in the art that various changes may be made in the procedural steps, proportions of ingredients and other process conditions disclosed hereinbefore, without departing from the spirit of this invention and the scope of the appended claims.

Having now described'our invention, we claim:

1. The method of making a stiffened corrugating medium comprising the steps of forming a paper sheet from an aqueous slurry of cellulosic fibers,

substantially drying said formed sheet,

applying to at least one surface of the paper sheet a solution containing waste pulp liquor solids, thereafter completing the drying of the paper sheet and fiuting said sheet.

2. The method of claim 1 wherein the solution comprises waste sulfite liquor.

3. The method of claim 1 wherein the solution comprises waste kraft liquor.

4. The method of claim 1 wherein the solution comprises desugared pulp lignin.

5. The method of claim 1 wherein said solution has a solids content ranging from 5-25% by weight, and in which 0.5 to 15% by weight, dry fiber basis, of said solids is added to said paper.

6. The method of claim 1 wherein the solids content of said solution is about 15 by weight, and about 3% by weight, dry fiber basis, of said solids is added to said paper.

References Cited by the Examiner UNITED STATES PATENTS 2,849,314 8/1958 Goss 162-163 FOREIGN PATENTS 587,237 11/1950 Canada.

DONALL H. SYLVESTER, Primary Examiner.

H. R. CAINE, Assistant Examiner. 

1. THE METHOD OF MAKING A STIFFENED CORRUGATING MEDIUM COMPRISING THE STEPS OF FORMING A PAPER SHEET FROM AN AQUEOUS SLURRY OF CELLULOSIC FIBERS, SUBSTANTIALLY DRYING SAID FORMED SHEET, APPLYING TO AT LEAST ONE SURFACE OF THE PAPER SHEET A SOLUTION CONTAINING WASTE PULP LIQUOR SOLIDS, THEREAFTER COMPLETING THE DRYING OF THE PAPER SHEET AND FLUTING SAID SHEET. 